Not good form to get upset and act all irritated at the dealer's service guys. It's not their fault after all.
There are a lot of things that could cause that light shredding. As mentioned earlier, pulley alignment, tensioner and idler should all be checked. But it could have been a stone that got kicked up at one time.
Also, cheap belts will do that very quickly. I've learned the hard way to buy only the best brand that you can when replacing, like Gates.
2005 4.0 MT dual exhaust GT mufflers GT suspension and wheels